The invention also relates to a cover for an electrical assembly, wherein the assembly has a substrate and at least one component mounted on said substrate. The cover has a support surface by way of which said cover can be placed onto the substrate. Furthermore, the cover has a cavity in which the component can be received. The component has contact both on its top side and on its bottom side by way of which said component is mounted on the substrate. Said contacts are thus situated at different joining levels.
The joining levels are defined in that, during the mounting on a substrate and during the establishment of contact, the contact of electronic components are situated on different planes, wherein here, the expression plane is meant in the technical sense rather than the mathematical sense. A plane, or the associated joining level, defines regions in which certain electrical or other mechanical connections of the components to be contacted are situated. By way of the arrangement of components one above the other, the joining levels are preferably likewise situated one above the other, in particular in a parallel orientation with respect to one another.
Methods for the mounting of electronic components on substrates are known. Said mounting methods are also used in the mounting of electronic assemblies in the power electronics field. For example, DE 100 62 108 A1 describes that a power module can be formed in the case of which the electronic power components can be connected to the substrate by way of a sintered layer. The substrate may involve DCB (direct copper bond) ceramic substrates such as are commonly used in the power electronics field. The top sides of the power components could be connected by way of a sintered layer to, for example, an additional thermal capacity, which provides a cooling body. Likewise, the substrate may, by way of its bottom side, be connected by way of a sintered layer to a further cooling body.
From DE 10 2007 047 698 A1, it is known that the sintered connections of electronic assemblies can be manufactured with the aid of special tools. Said tools have pressure surfaces which make contact with the component parts to be sintered, such that, during the sintering treatment, a pressure can be exerted on said components. By way of tolerance compensation in the tool, it can be ensured that the applied pressure is uniform even if the assembly to be sintered has tolerance-induced manufacturing inaccuracies. During the sintering treatment, in addition to the pressure build-up, it is necessary for a certain sintering temperature to be attained over a defined period of time. It is also possible for soldered connections to be provided instead of sintered connections.
According to US 2013/0201631 A1, it must be ensured that the temperatures required for the sintering process are selected such that joining connections that have already been produced in the assembly are not melted again by the heat treatment presently taking place. This is achieved in that the component connections already formed before the respective connecting process have connecting materials whose process temperatures (softening temperature, sintering temperature, melting temperature) lie, with a sufficient safety margin, above those process temperatures of the connecting process presently taking place. In this way, the joining connections that have already been formed are not put at risk, in terms of their integrity, by the connecting process presently taking place.
After the components have been mounted on the substrate, it is generally also necessary for contacting of said components to the substrate to be realized by way of suitable contacting structures. Here, contacts situated on the top side of the component are connected to corresponding contacts on the substrate. For this purpose, aside from the generally known bonding wires, it is also possible, as per US 2012/0106109 A1, for use to be made of metallic conductive structures which may for example be part of a leadframe. The suitably bent conductive structures are preferably connected to the respective contact surfaces by way of sintering or soldering. Another possibility consists in providing the contacting structures by way of flexible foils onto which the conductive structure is printed, for example. The flexible foils may also be connected, as per DE 10 2009 016 112 A1, to the respective contact surfaces of the top side of the component and to the mounting side of the substrate by way of sintered connections.
Owing to the levels of electrical power implemented in power electronics structures, the power electronics assemblies are subjected to high thermal and electrical load, as a result of which the electrical connections and other joining connections must exhibit high reliability. Sintered connections in particular are particularly suitable for this purpose because their thermal stability, and flawless formation of the joining connection, can be ensured. However, the mounting of power electronics assemblies by way of sintered connections presently entails a certain amount of additional outlay in terms of manufacture, for example in relation to soldering.